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Sunday, September 19, 2021

New research: Stars can experience their own kind of midlife crisis

At about the age of our Sun, the magnetic field generation mechanism of stars suddenly becomes sub-critical or less efficient.

By: Science Desk | Kochi |
July 28, 2021 4:10:31 pm
SunHighEnergyRaysX-rays stream off the Sun in this image showing observations by NASA's Nuclear Spectroscopic Telescope Array, overlaid on a picture taken by NASA's Solar Dynamics Observatory (NASA/JPL-Caltech/GSFC)

If you thought a midlife crisis during the pandemic was the worst, we have encouraging news: You are not alone. Middle-aged stars have a similar crisis period where they experience breaks in their activity and show slow rotation rates. The new study published today adds that our Sun may be currently transitioning to a magnetically inactive future.

As stars age, they experience a ‘magnetic braking’, causing them to gradually slow down their rotation. This slow rotation also alters its magnetic fields. The number of stellar activities – sunspots, flares, outbursts – also reduce. This slowing down is expected to be smooth and predictable and over the past two decades, researchers have studied the rotation period of a star to estimate its age.

However, recent observations show that this relationship between rotation period and age breaks down around middle age. The new work provides an explanation for this. It was published in Monthly Notices of the Royal Astronomical Society and carried out by researchers from the Indian Institute of Science Education and Research (IISER) Kolkata.

“Using dynamo models of magnetic field generation in stars, the team shows that at about the age of the Sun, the magnetic field generation mechanism of stars suddenly becomes sub-critical or less efficient,” explains a release from the Royal Astronomical Society. “This allows stars to exist in two distinct activity states – a low activity mode and an active mode. A middle-aged star like the Sun can often switch to the low activity mode resulting in drastically reduced angular momentum losses by magnetised stellar winds.”

The new work also provides insights into the low activity episodes seen in our Sun in the recent past. Known as the Solar Minimum, the period has very few solar activities such as sunspots. The best example of solar minimum was the Maunder Minimum which occurred around 1645 to 1715 during which very few sunspots were seen.

The corresponding author of the work, Prof Dibyendu Nandy from the Center of Excellence in Space Sciences India and Department of Physical Sciences at IISER Kolkata, comments in the release: “This hypothesis…provides a self-consistent, unifying physical basis for a diversity of solar-stellar phenomena, such as why stars beyond their midlife do not spin down as fast as in their youth, the breakdown of stellar gyrochronology relations, and recent findings suggesting that the Sun may be transitioning to a magnetically inactive future.”

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